Light-emitting diodes are energy efficient, have a long service life, and have been used extensively for outdoor lighting. Since light emitted by a conventional light-emitting diode is relatively focused, a secondary light distribution technique, e.g., use of a secondary optical lens, can be employed to provide a more uniform light distribution for applications in roadway illumination. The light emitted by the conventional light-emitting diode is refracted upon entering the secondary optical lens, therefore, design parameters such as curvature and thickness of the secondary optical lens may be manipulated for achieving a more uniform light distribution or for forming a desirable light distribution pattern.